A hollow wood golf club head of which face portion is made of a low-specific-gravity material having a specific gravity of 4.0 or less such as an aluminum alloy or a magnesium alloy has been proposed (see, paragraph 0028 of the following Patent Document 1). This type of golf club head can allocate more mass to the back of the face portion in exchange for lightening the face portion. Therefore, this kind of golf club head provides a large moment of inertia, and the effect of stabilizing the direction of the hit ball is expected.
On the other hand, the tensile strength of such low-specific-gravity material is much smaller than that of high-specific-gravity materials (for example, titanium alloys etc.) having a specific gravity of more than 4.0.
For example, typical tensile strengths of the aluminum alloys and magnesium alloys are 470 MPa and 270 MPa, respectively, which are less than a half of the tensile strength of 960 MPa of a typical titanium alloy. Therefore, in order to manufacture a golf club head using the low-specific-gravity material for the face portion, it was necessary to configure the face portion with a considerably large thickness to satisfy the practical durability,    Patent Document 1: Japanese Patent Application Publication No. 2014-79447